A 1.0 L container holds a stoichiometric mixture* of ethene (C2H4), ethane (C2H6) and
oxygen at a total pressure of 2.0 atm and a temperature of 25 °C. The mixture is ignited and
completely combusts to form carbon dioxide and water. The water is removed from the
vessel, leaving only carbon dioxide at a total pressure of 0.95 atm at the same conditions.
What is the mole fraction of oxygen in the original mixture?
 A stoichiometric mixture means a mixture where the mols of each gas are present in a ratio
proportional to the stoichiometric coefficients. Another way to think about it is that there is
enough oxygen to fully combust the ethene and ethane, but no extra.